As a method for producing an optically active amino acid amide and an optically active amino acid, there has been known, for example, an optical resolution method using an enzyme which enantioselectively hydrolyzes one of the optically active forms of an amino acid amide or using a microorganism containing the enzyme. This method is advantageous in that an optical resolution can be performed under a mild condition without use of expensive optical resolving agents and/or devices.
However, in the above-mentioned method of optical resolution of an amino acid amide using an enzyme that enantioselectively hydrolyzes an amino acid amide or a microorganism containing the enzyme, an unreacted optically active amino acid amide coexists with the optically active amino acid as a reaction product in the reacted solution, and thus it is necessary to separate the optically active amino acid amide and the optically active amino acid after the reaction. As a method of this separation, there is known a method of preferentially precipitating and filtering off an optically active amino acid by concentrating a reacted aqueous solution and then adding thereto an organic solvent or by concentrating the aqueous solution with addition of an organic solvent that forms azeotrope with water so as to replace the water with the organic solvent (refer to Patent Document 1).
However, when either of an acid or a base exists together with an optically active amino acid amide and an optically active amino acid in an enzymatically-reacted solution, it is difficult to separate the optically active amino acid amide and the optically active amino acid, because the optically active amino acid amide and the optically active amino acid form acid salts or base salts to become hardly soluble in the organic solvent. Further, when a salt is contained in the enzymatically-reacted solution, there is a problem that the salt is also precipitated together with an optically active amino acid that is obtained as an insoluble matter in the organic solvent, thereby lowering crystal purity and efficiency of collecting the amino acid separately from the optically active amino acid amide.
Patent Document 1: Japanese Patent Laid-open No. 2001-11034